During their manufacture, woven, knit, and piled conventional nylon fabrics undergo many types of dye processes to impart color for styling, aesthetics and other commercial requirements. Conventional nylon (anionic or acid dyeable) includes ordinary nylon 6 and nylon 66. As a result of industry tastes and individual preferences, the yarns in these fabrics are either dyed a single color, or two or more colors as part of a multicolored design.
If a fabric is dyed a single color, the fabric is likely to be dyed using either a batch or continuous dye method. Batch dyeing is a dyeing method that dyes a set amount of nylon, wool, or silk fabrics, yarns, or fiber stock as a single entity in an aqueous dye bath. The textiles are batch dyed in amounts up to 3-5 thousand pounds of goods, in 8-20 times that amount of water, which is referred to as the liquor ratio (water weight/fiber weight). Typically the chemicals found in a batch dye bath, aside from water, include anionic dyes, wetting agents, leveling agents and acid. The dyes may be either acid, direct, or fiber reactive and are typically present in an amount between 0.1 to 5.0% on weight of fiber (OWF), with 0.1% being for a light shade and 5.0% being for a dark shade.
The wetting agents in the bath are typically non-ionic surfactants for fast wetting and are present in an amount between 0.5 to 3.0% OWF. The leveling agents in the bath are typically cationic retarders for level dyeing and are present in an amount between 0.5 to 3.0% OWF. The acids in the bath are typically present in sufficient quantity to cause the pH of the bath to be between 7 and 3. Typically used acids include acetic acid, sulfamic acid, or MSP.
The liquor ratio of the dye bath is typically between 8 to 20, and the fibers are usually in the bath for 1 to 6 hours at a temperature of between 160 to 212.degree. F.
Continuous dyeing, in contrast to batch dyeing, is a dyeing method that disperses dye from an applicator onto a moving continuous web of fibers. The speed at which the web travels past the applicator can run between a few feet per minute to 100 yards or more per minute. The widths of webs can be a few inches to several yards.
The shade of the continuous dyed textile depends on the amount of dye in solution coupled with the amount of solution deposited onto the fiber web. Solution weight is referred to as wet pick up (WPU), that is the ability of the fiber web to pick up solution. WPU is therefore expressed as a percentage of fiber weight. Typically, the chemicals used in a continuous dyeing operation include anionic dyes, wetting agents, thickeners and acids.
The continuous dye solution typically has a WPU of between 50% to 300%. The anionic dyes are typically present in the continuous dye solution in an amount between 1 g/l to 50 g/l, where 1 g/l is for a light shade and where 50 g/l is for a dark shade. The dyes can be acid, direct or fiber reactive.
The wetting agents are typically non-ionic surfactants for fast wetting and are present in the continuous dye solution in an amount between 0.5 g/l to 5.0 g/l.
The thickener is typically present in the continuous dye solution in an amount between 2 g/l to 10 g/l and are often guar gums to reduce dye migration. The acids are present in the solution in a sufficient quantity to create a pH of between 5 to 2, and may include acetic acid, sulfamic acid, or MSP. The continuous dye solution is applied and the dye fixed between 1 and 20 minutes at a steaming temperature.
The continuous dyeing method can also be used to create multiple color fabrics. When the continuous dyeing method is used to create multi-colored fabrics, the applicator has different heads, with each head dispersing a different color pigment. Once colors are applied to a fabric by this method, the fabric cannot undergo a second dyeing process to add colors, as the colors would likely bleed or blend. Furthermore, it would be difficult to match up the design pattern with the applicator when applying another color at a later time. Even when the continuous dye method is used to create multi-colored fabrics, there is not a high degree of detail in a multiple colored pattern produced from this dyeing process.
Multiple color dye effects can also be achieved by other techniques. For instance, with the dye techniques known as package dyeing and space dyeing, strands of yarn are first dyed solid and multiple color shades respectively. The strands are then woven, knitted or tufted into patterns to produce a multicolored design. For the purposes of this application, by "woven" is meant the incorporation of a fiber or yarn into a fabric, and encompassing piled, tufted, sewn and knitted. All of these dyeing techniques require mills to maintain a large inventory of colored yarns in order to provide a large selection of fabrics. The techniques necessarily limit the speed of production since the fabrics must be created from different colored yarns each time a different color scheme is selected.
Another commercial method for creating multiple colored patterns uses dyes which are only attracted to specific types of fibers (fiber selective dyes). Using this method fabrics are first woven with different types of undyed fibers. They are woven in a pattern so that when the fibers are dyed, the finished product has a multicolored pattern. The fabric is then dyed with fiber selective dyes to color the different fibers in the fabric. Unfortunately, this method is expensive and is limited to a narrow range of color shades. Moreover, manufacturers that employ this method must maintain a wide array of yarns in inventory in order to use a variety of colors.
While it would seem more efficient to sequentially dye fabrics with a series of colors, there are practical reasons why this is not commercially viable. For instance, previously dyed fabrics tend to bleed when subjected to the high temperature conditions of a second dyeing step. When the fabrics bleed, the ionic bonds which typically hold acid dyes to nylon are broken, thereby releasing the dye molecules. Previously dyed fabrics also absorb dye from a second dyeing process which changes the color shade. However, these problems have recently been partially overcome.
One solution has been to use anionic solution dyed nylon fibers. Dye pigment is entrained in these nylon fibers during production of the fibers themselves. As a result, the coloring in solution dyed nylon does not wash out or bleed under dyebath conditions. Advantageously, solution dyed nylon tends to be naturally resistant to further dyeing by most anionic acid dyes, and therefore also functions as a partial stainblocker. As a result, if solution dyed nylon fibers are interspersed with conventional undyed nylon fibers, and both are later exposed to an anionic dye, only the undyed nylon fibers are dyed. A problem with solution dyed nylon however, does remain in that it is only manufactured in a limited number of solid shades. Since maximum styling capability requires predyed yarns available in a wide variety of colors and shade depths, solution dyed nylon only offers a partial solution.
Other multiple color fabric processes are disclosed in U.S. Pat. No. 5,445,653 to Hixson and in U.S. Pat. No. 5,484,455 to Kelley. These methods use certain fiber reactive dyes on CD-nylon fibers (cationic dyeable). Since conventional nylon 6 and nylon 66 fibers are cationic, with a high concentration of amine end groups (dye sites), they are readily dyeable by anionic acid dyes. In contrast, CD-nylon fibers are anionic with few amine end groups and thus few dye sites. While CD-nylon has the advantage of exhibiting inherent stainblocking ability as to acid stains, it is not as versatile in accepting dye colors as ordinary nylon.
Fiber reactive dyes are generally used on cotton and exhibit good colorfastness because of covalent bonds between the dye and the cotton. These covalent bonds are more difficult to break than are ionic bonds, which are typically associated with acid dyes on conventional nylon. Attaching fiber reactive dyes through covalent bonds to CD-nylon achieves both the colorfastness and dye resistance needed for a multiple color dyeing process. When fiber reactive dyes are used to dye CD-nylon fibers, and the CD-nylon fibers are later woven with conventional undyed nylon fibers, exposing the predyed CD-nylon fibers later to acid dyes will not dye the CD-nylon fibers.
Although fiber reactive dye methods for CD-nylon allow for the creation of predyed yarns, which later resist taking on acid dyes of a second dye step, the depth of color shades achievable with CD-nylon is limited. CD-nylon has very few amine end groups as compared to ordinary nylon. Since the fiber reactive dyes must attach themselves to these end groups in order to form a covalent bond, it is not possible to build the dye shades to dark and heavy colors. Furthermore, dyed CD-nylon fibers suffer from poor lightfastness, especially in light shades. Where CD-nylon is used as a natural stainblocker, there are also inherent limitations. As disclosed in U.S. Pat. Nos. 5,085,667, 5,199,958, 5,350,426 and 5,466,527 each to Jenkins, some acid and pre-metalized acid dyes will dye CD-nylon as well.
In summary, the problems associated with multiple color dye processes have prevented the use of sequential dye methods to produce multicolored fabrics. Those multicolored dye processes that have been used require large inventories of different yarns and have been limited to a small number of color shades. A need therefore remains for a multiple color dye process whereby woven nylon fabric can be subjected to sequential dyeing operations without dye bleeding or blending during a second dyeing step. A need also remains for a multiple color dye process which allows manufacturers to provide a broad selection of fabrics without having to warehouse large inventories. Accordingly, it is to the provision of such methods that the present invention is primarily directed.